1. Field of the Invention
The disclosed invention relates to a processor, particularly a processor that uses a power gating driving method.
Here, a processor means a processing unit having an arithmetic unit and a controller. For example, a microprocessor, a CPU, and an MPU are processors.
2. Description of the Related Art
These days, as a technology for downsizing a semiconductor element is improved, the integration degree of a processor such as a CPU or an MPU is markedly improved, and the processing speed of the processor is greatly increased. On the other hand, as the semiconductor element becomes small, the number of semiconductor elements provided in the processor greatly increases, and the power consumption of the semiconductor element due to leakage current markedly increases.
One of driving methods for reducing the power consumption of a processor is a method for driving a processor that is called power gating (hereinafter also referred to as a power gating driving method). A power gating driving method is a driving method in which in a period during which a processor does not need to perform arithmetic processing, supply of power to at least part of the processor is stopped to prevent consumption of wasted power.
A volatile memory element such as a register or an SRAM is usually used as a memory element in a processor. When supply of power to the processor is stopped by the power gating driving method, data in the volatile memory element provided in the processor is lost. In contrast, by providing a flash memory that is a nonvolatile memory element in a processor and writing data in a volatile memory element to the nonvolatile memory element when supply of power is stopped, the data can be retained (for example, see Patent Document 1).